We excised the central AGN and background point sources. Using the ciao tool specextract, we extracted the source, background spectra, and the response files of selected regions in the Chandra images separately for the three data sets.
The spectra for each data set were grouped so that each bin contained at least 20 counts. We restricted our spectral extraction in the energy range 0.5–7.5 keV, and fitted for the thermal gas emission with xspec [1]} using the isothermal apec model.
The abundance was fixed to 0.3 \(\times \)  solar [2]} and all spectral fits include absorption by the Galactic column [3]}.
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